Goodwill and intangible assets - Schedule of Goodwill (Details) $ in Millions	3 Months Ended
	Dec. 31, 2020 USD ($)
Goodwill [Roll Forward]
Beginning balance	$ 1,016.0
Cumulative translation adjustment	11.0
Ending balance	1,056.2
Americas
Goodwill [Roll Forward]
Beginning balance	865.8
Cumulative translation adjustment	0.1
Ending balance	895.1
International
Goodwill [Roll Forward]
Beginning balance	150.2
Cumulative translation adjustment	10.9
Ending balance	161.1
Formulations Acquisition
Goodwill [Roll Forward]
Goodwill acquired	29.2
Formulations Acquisition | Americas
Goodwill [Roll Forward]
Goodwill acquired	29.2
Formulations Acquisition | International
Goodwill [Roll Forward]
Goodwill acquired	$ 0.0